Seats in a motor vehicle are often at least adjustable in fore and aft directions (that is, towards the front and rear of the motor vehicle) by a seat track assembly. A lower seat track is affixed to the floor of the motor vehicle, either directly or mounted on a riser or other mounting assembly. An upper seat track is affixed to the underside of the vehicle seat, directly to a base of the seat or to an angled seat pan. The seat pan and the seat risers, where employed, allow the seat to be positioned at an angle and a height deemed most suitable for an occupant of the motor vehicle. For the front seats of a motor vehicle, typically two seat track assemblies are employed, one along each side of the seat base.
In seat track assemblies, frictional forces between the tracks must be minimized to allow position adjustment with acceptable efforts. U.S. Pat. No. 2,886,095 to Heyl shows a seat track assembly having an upper track sliding over a lower track. A pair of low friction washers is attached to rivets affixed to the upper track. The rivets slide back and forth in slots in the lower track, and the low friction washers slide over the lower track on the edges of the slots. Problems with this design include travel distance limited to the length of the slot and the potential for unacceptably high friction forces as the load is concentrated on the pair of washers. Moreover, the acceptable weight that can be placed on the seat track assembly may be restricted, since the load of the seat and any occupant in the seat all travels on the lower track which is weakened by the slot running down its middle. Additionally, wobbling of the seat may occur unless additional provision is made for lateral stabilization of the upper seat track relative to the lower seat track.
A more modern and structurally robust design is shown in U.S. Pat. No. 5,076,530 to Dove et al in which an upper track slides over a lower track on a pair of rollers positioned in a channel defined by the lower track. The rollers act as principal load bearing elements, and ball bearing positioned on either side of the rollers between flanges of the lower track and walls of the upper track serve to provide lateral stability to the upper seat track.
It would be desirable to eliminate the need for rollers while maintaining low friction forces when the upper track slides over the lower track, as the rollers add weight, cost and complexity. Moreover, rollers require grease or a similar lubricant, with the additional requirement that the design be modified to shroud the parts to prevent the occupant of a motor vehicle from contacting the grease. Rollers produce some noise and OEM automobile manufacturers are becoming increasingly stringent in their noise requirements. In addition, the rollers occupy space in the motor vehicle that could be saved or better used as a mounting location for the lower seat tracks and/or the lower seat tracks.
In view of the foregoing, it is an object of the present invention to provide a seat track assembly for use in a motor vehicle seat to provide for at least fore and aft adjustment of the seat, that is of a robust, low friction design and reduces noise during operation.
It is an additional object of the present invention to provide, at least in preferred embodiments, a seat track assembly that allows optimization in the mounting of the lower seat track to the motor vehicle.
It is an additional object of the present invention, at least in preferred embodiments, to provide a seat track assembly of reduced cost and complexity while enhancing manufacturability.
It is an additional object of the present invention, at least in preferred embodiments, to provide a seat track assembly that does not require the use of a grease to maintain low frictional forces between the tracks.
It is an additional object of the present invention, at least in preferred embodiments, to provide a seat having a rollerless, low friction seat track assembly.
It is yet another related object of the present invention to provide such a seat track assembly that is highly reliable in operation.